1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and particularly, to a semiconductor device in which a method of manufacturing a semiconductor chip is mounted facedown on a board in the form of a bare chip.
2. Description of the Prior Art
As for a semiconductor device in which a semiconductor chip is facedown connected to a board in the form of a bare chip, there has been hitherto known a semiconductor device having such a structure that soldering materials such as Sn/Pb or the like is supplied to pads of a board in advance and metal bumps formed on the electrodes of a semiconductor chip are connected to the pads of the board by melting the soldering materials.
Such a structure necessarily rises up the manufacturing cost of the semiconductor device because soldering materials is fed to the pads of the board, and thus low-cost semiconductor devices needing no soldering materials has been researched and developed.
Japanese Patent Laid-open Publication No. 5-36761 discloses a semiconductor device having a connection structure requiring no soldering materials. According to the connection structure of this semiconductor device, electrodes formed on a semiconductor chip and pads that are formed on a board are connected to each other through metal bumps by using the curing shrinkage force of thermosetting resin.
The conventional semiconductor device connection structure will be described with reference to the drawings.
FIG. 17 is a cross-sectional view showing the conventional semiconductor device connection structure disclosed in Japanese Patent Laid-open Publication No. 5-36761.
In this semiconductor device connection structure, metal bumps 7 composed of elastically-deformable soft metals are formed on electrodes 6 formed on semiconductor chip 4 in order to connect the electrodes 6 of the semiconductor chip 4 with connection pads 8 of board 5. Thermosetting type resin 10 is inserted between the semiconductor chip 4 and the board 5.
Subsequently, the metal bumps 7 on the electrodes 6 and the connection pads 8 are confronted to each other, and then the semiconductor chip 4 is mounted on the board 5 so that the metal bumps 7 and connection pads 8 are brought into close contact with each other. Further, the structure is heated while weight is applied to press the semiconductor chip 4, whereby the resin 10 is cured, the metal bumps 7 are elastically deformed and the metal bumps 7 and connection pads 8 are brought into close contact with each other by the repulsive force of the metal bumps 7 to connect them.
Further, Japanese Patent Laid-open Publication No. 5-343473 discloses another conventional semiconductor device. In this case, the following method is used:
That is, electrodes of a semiconductor chip are positioned onto metal bumps formed on a board and then pressed until film-shaped insulating adhesive which is beforehand attached to the board or semiconductor chip is discharged from the gap between the semiconductor chip and the board, and at the same time the insulating adhesive is cured. In consequence, the semiconductor chip is fixed and connected to the board.
A first disadvantage of the above prior arts resides in that electrical connection cannot be kept with time lapse or under a high-temperature atmosphere. This is because the resin is used for the connection between the semiconductor chip and the board and the shrinkage force of resin is used to connect the metal bumps formed on the electrodes of the semiconductor chip with the connection pads of the board.
When the semiconductor device is kept in this state for a long term, the shrinkage force of resin may be reduced due to plastic deformation of the resin, so that the connection cannot be kept. When the semiconductor device is exposed to a high-temperature atmosphere, the thermal expansion of resin acts so that the semiconductor chip and the board are separated from each other, and the metal bumps and the connection pads are separates from each other. Therefore, the electrical connection cannot be kept.
Further, in the case where the semiconductor device is subjected to a thermal impact test such as a temperature cycle test or the like and the check of the electrical connection is performed in a room temperature state, even when the connection portions are actually separated from each other and thus the electrical connection state is not kept in a high-temperature state, it is estimated as if the electrical connection state is kept when the temperature is returned to the room temperature. In this case, it is misjudged as if there is no trouble in connection state.
A second disadvantage resides in that when a heat-radiating device is required, for example, in such a case that a semiconductor chip having a large heating value is used, an excessive force may be applied to the semiconductor chip when the heat-radiating device is installed.
The reason is as follows:
In order to enhance the heat-radiation performance, it is preferable that the heat conduction distance from the semiconductor device to the heat-radiating device such as a heat sink or the like is set as short as possible. Therefore, it is desirable that the heat-radiating device is directly attached to the semiconductor chip. However, when it is directly attached to the semiconductor chip, the weight of the heat-radiating device must be supported by the semiconductor chip, and this may cause a connection failure and damage to the semiconductor chip.
Therefore, it is required that the heat-radiation device is fixed to another member such as a board or the like to prevent excessive force from being applied to the semiconductor chip. However, in this case, a space to fix the heat-radiating device is needed, and this loses advantages of the high-density mounting effect obtained by connecting the semiconductor chip in the form of a bare chip.